Diagnostic tool for well abandonment tool

ABSTRACT

A tool is provided for diagnosing the downhole source of a surface casing vent flow for remediation of an abandoned well. The tool is run into the bore, the tool having a stack of pleated rings slidably mounted on a tubular mandrel. The tool is actuated. One end of the stack is set to engage with the casing and the stack is compressed axially to expand the pleated rings expand the casing for diminishing casing/cement micro-cracks. If surface casing vent flow is reduced, the downhole source is identified for remediation and, if not reduced, the tool is released, traversed uphole and actuated again.

FIELD

The current disclosure is directed to a tool for diagnosing gas leakage prior to implementing abandonment procedures for plugging wellbores.

BACKGROUND

Wells access subterranean hydrocarbon formations for the recovery of oil and gas. Once the well is exhausted or other failures, procedures are in place to abandon the well while protecting other resources including the prevention of the contamination of potable water sources and preclusion of surface leakage. Abandonment procedures have been developed in the oil and gas industry including steps to prevent underground interzonal communication and fluid migration up the well and into shallow drinking water aquifers or to surface.

The Alberta Energy Regulator, Alberta Canada, currently requires that a “bridge plug” be installed in the well, ostensibly above any source of fluids, as the first step in well abandonment. The bridge plug comprises a mechanical tool having a body carrying slips and an expandable, elastomeric seal ring. The tool can be operated by a tubing string extending down from ground surface. The slips are expanded to engage the casing and secure the tool in place. The seal ring is expanded to seal against the casing's inner surface. The body and seal ring thereby combine to close and seal the cased bore.

During the conventional abandonment procedure the bridge plug is positioned and set at a pre-determined depth in the casing bore. A hydraulic pressure test is then carried out to determine if the bridge plug and well casing are competent to hold pressure. The pressure test is currently performed by filling the casing bore with water and applying pressure at 1000 psi for 10 minutes. After it has been determined that both the bridge plug and the casing above the bridge plug are competent, a column of cement (typically 40 feet in length) is deposited in the bore immediately above the bridge plug. Finally, the top end of the steel casing is cut off at a point below ground level and a vented cap is welded on the upper end of the casing.

However, problems can commonly arise over time with this system for plugging and abandoning wells. For example, the elastomeric element of the bridge plug may develop surface cracks or otherwise deteriorate and allow fluid to leak past it. Minute cracks may also develop in the cement column where the cement abuts the inside surface of the casing. Further, the cement sheath in the annulus, around the outside of the casing, can shrink and develop cracks. One or more of these defects can result in natural gas or other fluid leaking either up through the cased bore or along the outside surface of the casing. Such leakage indicates that the abandonment process has failed. This failure is commonly identified when vegetation surrounding the well at ground surface begins to die. A further remediation is required, but the problem is to determine where along the well is the fluid leaking.

Current detection of the location of leaks, using logging systems, is expensive and circumstantial, measuring parameters of the cased wellbore that are indicative of the potential for a leak, but not determinative. Logging systems in use include acoustic, video, caliper, neutron, gamma and the like. Often the tools are used on combination. Logs are sometimes run under pressure to heighten resolution in some circumstances. Accordingly the current logging systems result in diagnostic costs in the order of 25 to 75 thousand dollars.

Presently there are tens of thousands of wells in Alberta, Canada that have been abandoned. However, many have been identified as leaking fluid to ground surface. Therefore, there is a need in the industry for a means to economically and more accurately locate the source of a leak for proper abandonment plug procedures under the regulations.

If plug procedures are not successful, remedial work is required and retesting completed for packer isolation, all of which adds significantly to well abandonment costs.

SUMMARY

A diagnostic method is provided and described herein for testing Surface Casing Vent Flow (SCVF), the flow of fluid, such as gas and/or liquid or any combination thereof, out of the surface casing/casing annulus. Leaks from the annulus are often referred to as internal migration.

Leaks can also flow from the bore of the casing, the annulus between the casing and surface casing or both. The bore of the casing can be effectively remediated with repair or replacement of the bridge plug. Location of internal migration is more challenging. The regulator requires the annulus between the main casing and surrounding surface casing to be left open to atmosphere. The surface casing must be tested for a vent flow or gas migration and if SCVF or gas migration problem is detected, remedial repair is required.

Generally, a resettable, retrievable diagnostic tool is provided that can is placed in the cased wellbore and is effective to temporarily seal micro-leaks in annular cement about the casing. The tool effects an elastic expansion of the casing for affecting annular cement integrity.

The diagnostic tool is conveyed upon a tubular string of pipe lowered into the casing bore of a well. In an embodiment, the tool comprises a central tubular mandrel having a longitudinal bore and connected to the pipe string, an expansion packer such as a stack of pleated rings slidably mounted on the mandrel, and first compression plate mounted on the mandrel at one end of the stack and a second compression plate slidably mounted on the mandrel at the other end of the stack; and a releaseable slip assembly having a slip assembly for actuating the releasable slip assembly for releasable compression of the stack of pleated rings.

The tool can be positioned downhole and is actuated by means such as the tubular pipe string extending from a rig at ground surface.

The tool utilizes the slip assembly for locking the stack of pleated rings in the casing. The slip assembly is actuated between a run-in-hole (RIH), pull-out-of-hole (POOH) and SET position. Typically the slip assembly and first compression plate are positioned at an uphole end of the ring stack and the second compression plate is located at the lower end. An actuator housing is axially slidable over the mandrel and supports the slip assembly and one complementary portion of the J-Slot mechanism, in this case the pin. The other complementary portion, the J-Slot profile, is located on the mandrel. The lower, second compression plate is fixed to the mandrel.

As illustrated, and picking up at one stage of the slip assembly's continuous cycle, a pull up on the tubing string and mandrel to an extreme up position engages an uphole ramp surface of the first compression plate to set the slip assembly and fix the actuator housing in the casing. Drag blocks associated with the actuator housing ensure operation of the slip assembly. Uphole pull on the mandrel and downhole compression plate affixed thereto to compress the stack against the now-fixed upper compression plate, compressing the rings. The axially compressed stack of rings expands radially, engage and expand the casing for subsequent diagnostics of the annulus outside the casing.

Thereafter, a set down of the mandrel shifts the slip assembly to release the slips to a run in mode or a pull out mode

The mandrel and rings are formed of steel, the rings expanding the casing within its elastic range. The stack of pleated rings, held in a compressed expanded state, continue to interlock with and press against the surrounding casing wall, thereby maintaining the wall in an expanded condition.

In another aspect of the invention, a component assembly is provided having a stack of pleated steel rings, separated or bracketed by flat annular washers, which is slidably mounted on a mandrel between flat compression plates. The washers serve to distribute compressive force evenly to the pleated rings.

The rings are preferably dimensioned and configured so that they are insertable in the casing bore and yet, when compressed a suitable amount (e.g. 50%), they are operative to expand radially sufficiently to press against the casing wall and provide a circumferential frictional interlock or engagement with the casing.

In a further preferred feature, compression-resistant spacers may be positioned in varying amounts between the washers, so as to provide a characteristic of increasing resistance to radial expansion of the independent pleated rings whereby they expand in sequence from the first compression plate to the second compression plate.

In a further feature, a sleeve or shield surrounds the stack for minimizing interference with casing during the run in and pull out modes and for aiding in uniformity of compression of the pleated rings along the stack between the first compression plate to the second compression plate.

In summary, the diagnostic tool is characterized by metal-to-metal circumferential radial force application and frictional engagement of the rings with the well casing for affecting micro annular flow.

In still another aspect a method for diagnostic testing is provided by temporarily establishing a casing expander for influencing annular cement sealing in the course of establishing the success of a prior well abandonment and identifying the source of leaks in unsuccessful abandonments.

A method for identifying a source of surface casing vent flow comprises conveying a tool to traverse the well downhole to a specified location along the cemented portion of the casing and expanding the casing at the specified location for diminishing micro-leaks in the cemented annulus. Thereafter, one determines a change in the surface casing vent flow, such as through measurements of any flow at surface compared to flow prior to the testing. One can expand the casing by releasably locking the tool to the casing, and actuating the tool to expand into the casing for diminishing micro-leaks in the annulus about the casing.

The change in the surface casing vent flow can determined by, prior to actuating the tool, determining a first baseline surface casing vent flow, then after actuating the tool, determining a second surface casing vent flow; and comparing the difference in the first and second surface casing vent flows.

The tool can be conveyed on a string of tubing, traversing the well to the specified location. One shifts the tool from a run-in-hole (RIH) position to a SET position and actuates the tool in the SET position to lock a first end of the stack of pleated rings to the casing at the specified location and pulling on the string of tubing to compress the stack of pleated rings against the first end of the stack, expanding the pleated rings for expanding the casing. If the measured surface casing vent flow does not represent a change, then one shifts the tool from the SET position to a pull-out-of-hole (POOH) position to release the stack of pleated rings and traverse the well to an subsequent specified location uphole from the specified location; and repeat the, actuating of the tool and then measuring the surface casing vent flow.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1A is a one-quarter section, side view of one embodiment of the diagnostic tool in the downhole manipulation, run-in-hole (RIH) mode;

FIG. 1B is a one-quarter section, side view of the tool of FIG. 1A, after an intermediate downhole shift, then shown in an uphole manipulation to shift the tool for the next stage or to pull-out-of-hole (POOH), the profile preventing actuation of the slip assembly;

FIG. 1C is a one-quarter section, side view of the tool of FIG. 1A, after an intermediate downhole shift then shown in an uphole manipulation to engage the cone and set the slip assembly to engage the casing;

FIG. 2 is a rolled out plan view of a J-Profile of one embodiment of the J-Slot mechanism;

FIG. 2A is a partial, enlarged view of the slip assembly, including mandrel and actuator housing according to FIG. 1A, the slip assembly in a RIH position;

FIG. 2B is a partial, enlarged view of the slip assembly, mandrel and actuator housing according to FIG. 1B, the slip assembly in the POOH position;

FIG. 2C is a partial, enlarged view of the slip assembly, mandrel and actuator housing according to FIG. 1C, the slip assembly in a SET position;

FIG. 3 is a flow chart of a diagnostic procedure according to one embodiment;

FIG. 4A is a partial, enlarged view of the stack of pleated rings fit with a running shield, the tool in the POOH position;

FIG. 4B is a partial, enlarged view of the stack of pleated rings fit with the running shield of FIG. 5A, the tool in the POOH position with the shield engaged between the expanded rings and the expanded casing; and

FIG. 5 is a partial, enlarged view of the stack of pleated rings fit with a running shield, one discontinuous shield extending about the full circumference and split axially.

FIG. 6A is a side view of the rings of a portion of the tool in a cross-section of casing, and in one embodiment the stack of pleated rings having an increasing density of compression modifiers closer to the actuating end of the stack;

FIG. 6B is a close up view of adjacent pleated rings, such as those shown in FIG. 6A, the stack cut away above and below to illustrate the pleated rings separated by flat washers, having adjacent peaks and troughs misaligned, one spacer being illustrated in exploded view separate from the pleated rings, and a mandrel passing therethrough;

FIG. 6C is a close up view of adjacent pleated rings, according to FIG. 6B, with adjacent pleat peaks and troughs aligned;

DESCRIPTION OF THE EMBODIMENTS

Having reference to FIG. 1A, a diagnostic tool for manipulating the annulus about well casing is provided, typically used in a methodology for confirming integrity of an abandoned well or well to be abandoned or identifying the downhole location of annular fluid migration or leak path. The tool is sized for a cased well, such as that typically extending through a surface casing or other outer casing, forming an annulus that has been cemented and may not have retained its integrity, resulting in an internal leak path.

The tool 10 comprises a central tubular mandrel 14 attached and conveyed downhole of the bore 50 of the casing 54 on a string of tubing, such as jointed pipe or coiled tubing. A stack 16 of pleated metal pleated rings 18 is positioned on the mandrel 14. The rings 18 are separated and spaced apart by flat, annular washers 20. First and second annular compression plates 22, 24, having facing perpendicular shoulders, straddle or bracket the stack 16 at its upper/uphole and lower/downhole ends respectively. The stack of pleated rings is also described in companion international application PCT/CA2016/051429 filed Monday, Dec. 5, 2106 and claiming priority of CA 2,913,933 filed Dec. 4, 2015.

The second or downhole compression plate 24 is secured or fixed to the mandrel 14. Plate 24 can be secured with shear screws or other releasable fasteners as required for retrievability if the tool becomes stuck. The uphole compression plate 22 is axially slidable along the mandrel 14 and axially delimited on the mandrel by a shoulder 26 to pre-determine the uphole location thereon. The washers 20 and pleated rings 18 are slidably mounted on the mandrel 14 between the uphole and downhole compression plates 22,23.

Best shown in FIGS. 2A to 2C, an uphole slip assembly 30 is mounted to the mandrel 14 uphole of the stack of pleated rings 16. The slip assembly 30 determines the operation and release of slips 44 to lock the tool 10 against the casing 54. Generally, the slip assembly is releasably engageable with the inside wall 52 of the casing 54 and comprises a housing 32 slidable over the mandrel 14 for alternately releasing and compressing the stack of rings. A drag block 46 and slips 44 are supported by the housing 32. A pin 42 and slot assembly is located between the housing 32 and the mandrel 14, the slot has a J-Profile 40 having at least a run-in-hole (RIH) position for spacing the slips from a slip cone 34, a pull-out-of-hole (POOH) position for spacing the slips from the slip cone, and a slip set (SET) position for engaging slips 44 with the slip cone 34 for axially compressing the pleated rings 18 between the first and second compression rings 22,24 for radially expanding the pleated rings.

The actuator housing 32 is axially slidable on the mandrel, all of which is uphole of the uphole compression plate 22. The uphole face of the upper compression plate 22 is a ramp-like surface or cone 34 compatible with the slips 44.

The actuator housing 32 is axially movable along the mandrel 14 as part of the slip assembly 30, variably delimited by cooperation of the pin 42 configured to follow the J-Profile 40. Drag blocks 46 are fixed axially within the housing 32, and are biased radially outwardly to the casing to enable shifting of the J-Profile with mere uphole and downhole manipulation of the mandrel.

The J-profile 40 and pin 42 alternately space the slip 44 from the cone 34 for free running in and out of the casing, or to enable axial engagement of the slips 44 with the cone 34 for slip actuation. As shown in this embodiment, the J-Profile 40 is formed in the mandrel 14 and the pin 42 is fixed to the housing 32

With reference to FIG. 2, the slot of the J-Profile 40 sequences four stages of operation or positions: in FIG. 2C, an uphole manipulation of the mandrel to pull the cone 34 into engagement with the slips (SET) at position C; in FIG. 2A, an downhole shift to position A to release the slips or run-in-hole RIH, in FIG. 2B an uphole pull of the mandrel to pull-out-of-hole POOH at position B with the slips spaced from the cone; and an intermediate downhole shift (A′) before the cycle repeats.

As shown in FIG. 6, the pleated rings 18 are formed of corrosion-resistant material, such as stainless steel. Each pleated ring 16 is sized for a sliding fit on the mandrel 14 and are dimensioned and configured so that they are insertable in the bore 50 of the casing 54 in their normal, pleated condition but, when compressed axially, for example partly compressed to about ½ of their axial height, they are capable of extending out radially sufficiently so as to reach the inside surface 52 of the bore 50 and to press firmly against it, thereby frictionally engaging it and slightly expanding the wall of casing 54, including the outer diameter of the casing into the annulus and any cement 56 therein. Simply, the uncompressed pleated rings have a first diameter less than that of the casing and when in the compressed position, the pleated rings have a second diameter adapted to engage the casing.

With reference to FIG. 6A, the stack 24 comprises flat annular washers 20 positioned between each adjacent pair of pleated rings 18. As shown in FIGS. 6B and 6C, the rings 18 can be oriented with their facing peaks 80 misaligned or aligned. As shown in FIG. 6B, if the peaks 80 of adjacent, facing pleated rings are misaligned, the intermediate flat washer is unsupported, and can be subject to deformation. As shown in FIG. 6C, if the peaks 80 of adjacent, facing pleated rings 18 are aligned, the intermediate flat washer 20 is supported between acting peaks and all the axially compressive force is transferred through the pleated rings. The flat washer can be steel or an elastomeric including Durometer 90 nitrile rubber.

Table 1 sets forth the relevant dimensional, material and compression data from a test in which a stack 16 of pleated rings 18 was mounted on a mandrel 14 and axially compressed within a 60″ length of oilfield 4.5″ steel casing 27 using a press.

TABLE 1 mandrel outside diameter - 2.5″ Each ring pleat height - 0.375″ casing inside diameter - 3.826″ ring material - 410 stainless steel casing wall thickness - 0.337″ ring wall thickness - 0.025″ casing outside diameter - 4.5″ Pleat spacers (copper tubing), 0.375″ diameter and wall thickness - 0.0625″ number of pleated rings - 10″ flat steel washer thickness - 0.125″ inside ring diameter - 2.5″ compressive force applied - ~27,000 lb/ft outside ring diameter prior to extent of stack length reduction - compression - 3.750″ about 40% outside ring diameter Result: Casing expansion - (unconstrained) after compression - 3.834″ about 0.008″. (Δ0.084″)

The test showed that the stack of rings outwardly bulged the adjacent casing wall by about 0.008″. Testing confirms that suggests the stacked-ring packer can be set and released multiple times in a single run.

Operation

A method is provided for identifying a source of surface casing vent flow from an abandoned well. Typically the wells are completed with casing and have a cemented annulus about at least a portion thereof.

The method comprises conveying a tool to traverse the well downhole to a specified location along the cemented portion of the casing, expanding the casing at the specified location for diminishing micro-leaks in the cemented annulus; and then determining a change in the surface casing vent flow. The tool can be conveyed on a string of tubing for traversing the well to the specified location and for shifting the tool from a run-in-hole (RIH) position to a SET position; actuating the tool in the SET position to lock a first end of a stack of pleated rings to the casing at the specified location; pulling the string of tubing to compress the stack of pleated rings against the first end of the stack, expanding the pleated rings for expanding the casing; and then thereafter measuring the surface casing vent flow.

As above, the expanding the casing comprises adjusting the tool from a traversing the well mode to a setting the tool mode for releasable locking the tool to the casing; and actuating the tool to expand into the casing for diminishing the micro-leaks.

One can determine a change in the surface casing vent flow by, prior to actuating the tool, determining a first baseline surface casing vent flow. Then, after actuating the tool, determining a second surface casing vent flow and comparing the difference in the first and second surface casing vent flows.

In greater detail, tubing conveys the tool downhole; the mandrel connected in the string of tubing, typically adjacent the downhole end thereof. The mandrel 14 serves to support the stack 16 of pleated rings 18. Actuation of the tool 10 is carried out by manipulating the tubing string from surface which manipulates the mandrel 14. Simply, the tool is RIH to a specified location, actuated to expand the casing, surface casing vent flow is monitored and if the flow is not significantly altered, the tool would be too low in the well to have intercepted the leak. The tool can be moved further uphole and the test is repeated.

Again, and with reference to FIG. 2 and FIGS. 2A, 2B and 2C, the mandrel is manipulated downhole and the tool is RIH (A′) to the specified location in the well casing. The mandrel is pulled up to SET (C) and pulled up further at a tension sufficient to expand the casing and affect the cement the annulus. Once the surface casing vent flow test is complete, which can be hours, days or weeks, the mandrel is set down again to the intermediate shift position A to continue downhole RIH, or merely to shift to pull up again (B) and POOH.

In order to ascertain the magnitude of the leak and determine if the diagnostic tool has identified a well location of interest, a baseline SCVF can be obtained. This can include a quantitative test, using a vent testing device including a meter, for measuring the SCVF such as in cubic meters per day. Such a test can take place over days or weeks.

Using a plan for tool locations, a first specified position is identified, the slip assembly is shifted to the RIH position and the diagnostic tool is run downhole to the selected, specified, pre-determined depth. The conveyance tubing is shifted to the SET position. The conveyance tubing is pulled up to set the slips, locking the uphole compression plate to the casing. The mandrel is pulled uphole to pull the cone against the slips and set the tool in the casing. One continues to pull the mandrel uphole and, as the uphole compression plate is arrested axially in the casing, the mandrel pulls the downhole compression plate against the stack against the uphole compression plate, compressing the pleated rings. The axially-compressed stack of rings expands radially, engages and expands the casing for subsequent diagnostics. As discussed, the rings expand the casing within its elastic range. The slip, uphole compression plate and moving downhole compression plate, compress the stack sufficiently so as to cause the pleated rings to partly flatten, expand radially, press against the adjacent casing wall and effect a metal-to-metal circumferential frictional engagement with the casing. The stack of pleated rings, held in a compressed expanded state, continue to interlock with and press against the surrounding casing wall, thereby maintaining the wall in an expanded condition.

The casing is expanded into the annular cement. Micro leak paths typically occur in the cemented annulus between the casing exterior and the wellbore. By expanding the casing, once can compress and aid the sealing of these micro-annular leak paths, uphole leakage therethrough to surface being temporarily reduced or blocked.

The stacked-ring packer has a myriad of interstitial spaces that will allow flow on the inside of the casing. If the upper compression plate includes an elastomeric packer, such as that between cone and the compression ring, casing bore sealing could similarly be effected in addition to annular sealing. Elastomeric packer compression could be delimited by stops along the mandrel to avoid over compression when actuating the more robust stack.

One maintains uphole tension on the conveyance string and mandrel to hold the stack in place and expansion of the rings. If the selected location in the well is at or above the leakage along the annulus, the leakage should be lessened, reducing the flow.

At surface, the SCVF leakage is measured over time. In general confirmation, any SCVF issues are usually visible at surface with a simple bubble test. As there can be a lag between restriction of any leaks and the flow at surface, the operator will wait a commensurate period of time before conduction this qualification test. Water is poured around the casing and bubbles can be seen or alternately the casing vent valve is opened and a hose from the line fed into a water bath and bubbles observed.

Alternatively a more quantitative test can be performed, using a vent testing device including a meter, for measuring the SCVF such as in cubic meters per day. Electronic detection equipment may be used, including sophisticated detection equipment coupled with analysis to compare gas chemistry to identify production zones to determine the source of the gas. Tests can take place over days to weeks.

If one determines a reduction in SCVF has been achieved, the leak has been identified and remediation could be applied. However, the testing has determined that the leak is at or even lower than the selected test location. Depending on regulations in place for the well location, including consideration of the identified location relative to the depth of ground water, and other considerations, one may need to run deeper in hole. One could then shift the tool to RIH, move the tool the a subsequent, lower selected location and repeat the testing.

If the identified location was at acceptable depth, remediation could occur, using one of the established methods for re-abandonment including Applicant's co-pending application PCT/CA2016/051429 utilizing a tool in combination with an elastomer applied through ports formed in the casing or more conventional cement squeezes through perforations, abrasajet cuts or section milling of casing.

If, at the selected location, the testing did not reduce the SCVF below a threshold, then the leak is uphole of the selected location

In this instance, the tool is shifted to POOH and moved uphole. In releasing the tool, the conveyance tubing is manipulated downhole, driving the lower compression plate downhole, decompressing and lengthening the stack and shrinking the pleated rings in diameter. Shortly thereafter, the cone pulls away from the slips and the tool is released from the casing.

If the stack of pleated rings are at all damaged, such as by a bore pressure test when set, the tool could be tripped out for repair or replacement. If moved, the tool could be located at the subsequent selected location and the set, test and surface measurement repeated again.

The tool is run to higher location if necessary, and repeat the setting, testing and releasing as necessary. When the tool is actuated, and SCVF continues, then the diagnostic tool is deemed to below the source of the leak as it was ineffective in blocking or restricting the leak path. The tool is successively moved uphole and set and SCVF measured until the source is located. The location and relocation of the diagnostic tool can be made on an incremental stepwise basis, or more informed or substantive moves can be made based on well logs or other known well characteristics.

Once complete, or for tool recovery, one pulls up on conveyance tubing to shift the slip assembly for POOH.

Release of tension on the conveyance tubing, permits the lower compression plate to release the stack, the upper cone to release from the slip and tool to be released from the well. The ring stack lengthens and reduces in diameter, releasing from the casing wall.

In short, and with reference to the flow chart of FIG. 3, and with reference to the tool positions as shown in FIGS. 1A through 2C, a baseline of the SCVF for the leaking well is established, typically using a vent metering device. This could take days to establish a base rate. Thereafter, the diagnostic tool is first located in the lower wellbore, surface flow tested, and if the leak was not already located, then the operator sequentially moves the tool upward, targeting likely areas such as shallow gas zones that were not ever produced, or where previous well data may suggest likely areas of sources. Depending on the nature of the leak the tool may be left in position for minutes, hours or days.

Operation of the stack of pleated rings can be optimized to minimize hang-up on casing interfaces and assist with uniform actuation of the rings along the stack.

In one embodiment, as shown in FIGS. 4A and 4B, one or more sleeves or shields can be wrapped circumferentially about the stack 16.

Two or more elongate leaves 60 can be secured at a first end at the first compression plate 22 and extend axially along the stack of pleated rings to a second end adjacent the second compression plate 24. Each leaf being arcuate and extending circumferentially about a portion of the circumference of the stack of pleated rings. Each leaf further comprises a guide extending axially from the second end; and a bracket at the second compression plate through which the guide extends slidably and restraining the guide radially to the second compression plate.

As stated, and in more detail with reference to the figures, axially elongate leaves 50 are secured at a first end at the first compression plate 22 and extend axially along the stack of pleated rings to a second end adjacent the second compression plate 24, each leaf 60 being arcuate and extending circumferentially about at least a portion of the circumference of the stack 16 of pleated rings.

As shown in FIG. 5, a single leaf can be typically split longitudinally, such as encompassing about a 340 degree wrap or full wrap, to enable circumferential expansion with the stack is actuated.

In the case of two or more independent leaves 60,60 . . . . The material is are inherently expandable circumferentially and with respect to each other when expanded radially with the pleated rings. Each leaf 60 further comprises a guide or leg 64 extending axially from the second end and a bracket 66 located at the second compression plate 24 through which the leg extends slidably for restraining the guide radially to the second compression plate 24. The leaves 60 aid the movement of the pleated rings 15 within the stack 16 and also the entirety of the stack of pleated rings of the tool along the casing 54, where otherwise the rings or spacers are otherwise prone to catch on inner casing features including collar interfaces.

When the stack is actuated to expand the casing, the leaves 60 are sandwiched between the pleated rings 18 and the casing 54.

Similarly, on this or other downhole tools using a compressive stack of pleated rings for casing sealing or expansion, a leaf 60 or leaves 60,60 . . . can also be provided for improved traversing and uniformity in actuation.

In another embodiment, as shown in FIGS. 6B and 6C, the stack 24 can further includes compression-modifying or resistant spacers 82 positioned between pleats and the flat washers 7. The spacers 82 are distributed in varying concentrations or density that diminishes upwardly from the downhole compression plate 24 to the uphole compression plate 22. The uphole compression plate becomes locked or fixed to the casing when the slips are set, and stack actuation occurs from the downhole compression plate up towards the uphole plate. The concentrations and distributions are selected so as to facilitate the desired sequential compression of the rings 18 from the stack's fixed end 24. The spacers 82 can be formed of short lengths of copper tubing 82T. The compression spacers 82 provide a characteristic of increasing resistance to compression of the individual pleated rings from the uphole compression plate 22 to the actuated compression plate 24. Thus the pleated rings 18 that are sliding along the mandrel 14, at the uphole end in this case, and relative to the casing 54, from the actuated compression plate 24 towards the fixed compression plate 22, are the last to be compressed. The pleated rings 18 of the stack 16 therefore expand in sequence to control the drag of the expanding rings as they are axially compressed. 

We claim:
 1. A downhole tool conveyed into a casing of a well on a string of tubulars extending downhole into the cased well from surface, comprising: a tubular mandrel releasably connected to the string of tubulars; a stack of pleated rings slidably mounted on the mandrel; a first compression plate slidably mounted on the mandrel at one end of the stack and having a slip cone; a second compression plate mounted on the mandrel at another end of the stack with the stack of pleated rings sandwiched therebetween; and a releasable slip assembly comprising a housing slidable over the mandrel for alternately releasing and compressing the stack of rings, a drag block and slips supported by the housing, and a pin and slot assembly between the housing and the mandrel, the slot having a profile having at least a run-in-hole (RIH) for spacing the slips from the slip cone, a pull-out-of-hole (POOH) for spacing the slips from the slip cone, and a slip set (SET) position for engaging slips with the slip cone for axially compressing the pleated rings between the first and second compression rings for radially expanding the pleated rings.
 2. The tool of claim 1, wherein the mandrel has a stop formed thereon for spacing of the slips from the slip cone in the RIH and POOH positions.
 3. The tool of claim 1, wherein in the released position, the stack of pleated rings have a first diameter less than that of the casing and when in the compressed position, the stack of pleated rings has a second diameter adapted to engage the casing.
 4. The tool of claim 3, wherein the second diameter of the stack of pleated rings is radially expanded to close the bore of the casing at a sealing location in the well.
 5. The tool of claim 3, wherein the first compression plate is uphole of the second compression plate; an uphole movement of the tubular with the releaseable slip assembly in the SET position axially compressing the pleated rings.
 6. The tool of claim 1, wherein the stack of pleated rings further comprises: a plurality of the pleated rings; and a plurality of flat washers, also slidably mounted on the mandrel, each flat washer axially separating a pair of adjacent pleated rings.
 7. The tool of claim 1 further comprising two or more elongate leaves, secured at a first end at the first compression plate and extending axially along the stack of pleated rings to a second end adjacent the second compression plate, each leaf being arcuate and extending circumferentially about a portion of the circumference of the stack of pleated rings.
 8. The tool of claim 7, wherein each leaf further comprises: a guide extending axially from the second end; and a bracket at the second compression plate through which the guide extends slidably and restraining the guide radially to the second compression plate.
 9. The tool of claim 1 further comprising a plurality of compressible spacers, each spacer sized to fit radially within a pleat of a pleated ring, wherein the spacers are fit to one or more pleats of a plurality of pleated rings in a population distribution that varies from a sparse concentration adjacent to the first compression plate, for providing a first resistance to compression, to a dense concentration adjacent to the second compression plate, for providing a second resistance to compression, the first resistance being less than the second resistance for providing an generally equal compression of the pleated rings along the axial extent of the stack.
 10. The tool claim 1 wherein: the pleated rings are formed of steel; and the diameter of the uncompressed pleated rings are dimensioned so as to be insertable in the bore of the well casing and are expandable upon compression in the stack to engage the casing wall.
 11. A method for identifying a source of surface casing vent flow from an abandoned well completed with casing and having a cemented annulus about at least a portion thereof, the method comprising: conveying a tool to traverse the well downhole to a specified location along the cemented portion of the casing; expanding the casing at the specified location for diminishing micro-leaks in the cemented annulus; and then determining a change in the surface casing vent flow.
 12. The method of claim 11, wherein the conveying the tool to the specified location and expanding the casing comprises: adjusting the tool from a traversing the well mode to a setting the tool mode for releasable locking the tool to the casing; and actuating the tool to expand into the casing for diminishing the micro-leaks.
 13. The method of claim 12, wherein determining a change in the surface casing vent flow comprises: prior to actuating the tool, determining a first baseline surface casing vent flow; after actuating the tool, determining a second surface casing vent flow; and comparing the difference in the first and second surface casing vent flows.
 14. The method of claim 12, wherein actuating the tool to expand into the casing comprises: setting a first compression plate at a first end of an axial stack of pleated rings on the tool to lock to the casing; and axially manipulating a second compression plate relative to the casing to axially compress and expand the stack of pleated rings to expand the casing.
 15. The method of claim 11, further comprising: conveying the tool on a string of tubing; traversing the well to the specified location; shifting the tool from a run-in-hole (RIH) position to a set (SET) position; actuating the tool in the SET position to lock a first end of a stack of pleated rings to the casing at the specified location; pulling the string of tubing to compress the stack of pleated rings against the first end of the stack, expanding the pleated rings for expanding the casing; and then measuring the surface casing vent flow.
 16. The method of claim 15, wherein if the measured surface casing vent flow does not represent a change, then further comprising: shifting the tool from the SET position to a pull-out-of-hole (POOH) position to release the stack of pleated rings; traversing the well to an subsequent specified location uphole from the specified location; and repeating the shifting of the tool to the SET position, actuating the tool to lock the first end of the stack of pleated rings to the casing at the subsequent specified location, pulling the string of tubing to compress the stack of pleated rings for expanding the casing; and then measuring the surface casing vent flow.
 17. The method of claim 16, wherein if the measured surface casing vent flow does change, then further comprising: identifying the downhole source of the surface casing vent flow being downhole of the specified location; and shifting the tool from the SET position to a POOH position to release the stack of pleated rings and convey the tool out of the well.
 18. A downhole tool conveyed into a casing of a well on a string of tubulars extending downhole into the cased well from surface, comprising: a tubular mandrel releasably connected to the string of tubulars; a stack of pleated rings slidably mounted on the mandrel; a first compression plate slidably mounted on the mandrel at one end of the stack and slip assembly for releasable engagement with the casing; a second compression plate mounted on the mandrel at another end of the stack with the stack of pleated rings sandwiched therebetween; and one or more elongate leaves, secured at a first end at the first compression plate and extending axially along the stack of pleated rings to a second end adjacent the second compression plate, each leaf being arcuate and extending circumferentially about a portion of the circumference of the stack of pleated rings.
 19. The tool of claim 18, wherein each leaf further comprises: a guide extending axially from the second end; and a bracket at the second compression plate through which the guide extends slidably and restraining the guide radially to the second compression plate. 